The present invention relates to pressure sensors. More specifically, the present invention relates to pressure sensors of the type which use a deflectable diaphragm to measure a pressure.
Transmitters are used in process monitoring and control systems to measure various process variables of industrial processes. One type of transmitter measures pressure of process fluid in the process. Various techniques have been used in the pressure sensors used in such transmitters. One well known technique is to use a deflectable metal diaphragm. A capacitance is measured with respect to the diaphragm, with the metal diaphragm forming one of the capacitive plates of the capacitor. As the diaphragm is deflected due to applied pressure, the measured capacitance changes. In such a configuration, there are a number of sources of inaccuracies in pressure measurements.
One technique which addresses these inaccuracies is set forth in U.S. Pat. No. 6,295,875 entitled, “PROCESS PRESSURE MEASUREMENT DEVICES WITH IMPROVED ERROR COMPENSATION” issued Oct. 2, 2001 to Frick et al. which is incorporated herein by reference in its entirety. This patent describes a differential pressure sensor that includes an additional electrode for use in reducing measurement inaccuracies.